1. Field of Invention
The present invention relates to a touch panel and, in particular, to a touch panel with enhanced transmittance.
2. Related Art
Recently, touch panels have been widely applied to typical consumer electronic products such as a mobile communication, a digital camera, a digital music player (MP3), a personal digital assistant (PDA), a global positioning system (GPS), a hand-held personal computer (hand-held PC) or a novel ultra mobile personal computer (UMPC). In each of the above-mentioned electronic products, the touch panel is a touch screen combined with a display screen. However, the reflectance of the touch panel significantly influences the viewing quality for the user.
Referring to FIG. 1, a conventional touch panel 1 mainly includes two transparent conductive films 11A and 11B disposed opposite to each other. The transparent conductive films 11A and 11B are separated by a plurality of spacers 12 with an air layer 13 formed between the transparent conductive films 11A and 11B. In addition, the touch panel 1 further includes a glass substrate 14, a plastic substrate 15 and a hardened layer 16. The glass substrate 14 is disposed on one side of the transparent conductive film 11A, and the plastic substrate 15 and the hardened layer 16 are disposed on one side of the transparent conductive film 11B. In addition, a display screen (not shown) can be connected to the glass substrate 14 to form a touch screen together with the touch panel 1.
However, the typical material of the transparent conductive films 11A and 1B is indium tin oxide (ITO) having a refractive index of about 2. The air layer 13 has the refractive index of 1, and the difference between the refractive indices of the transparent conductive films 11A and 11B and the air layer 13 increases the reflectance and thus lower the transmittance. In addition, the difference between the refractive index of the outside air and the refractive indices of the glass substrate 14, the plastic substrate 15 and the hardened layer 16 also increases the reflectance. FIG. 2 shows the relationship between the reflectance of the touch panel 1 and the incident light wavelength. As shown in FIG. 2, the average reflectance of the touch panel 1 is about 20% and may reach as high as 40%. Consequently, both the transmittance and the contrast of the touch panel 1 are decreased and the display quality is thus influenced.